This invention relates to a filter drier for the refrigerant of a refrigeration system, and more particularly, relates to a filter drier for installation in a liquid line of a refrigeration system for filtering and drying the refrigerant when the refrigerant is in a liquid state.
A refrigeration system, such as in an air conditioner or in a refrigeration unit, normally utilizes a filter drier for removing moisture and acids from the refrigerant and for filtering particles of metal, dirt, or grit from the refrigerant thereby to prevent damage to operation of the compressor and other components of the refrigeration system having movable parts or close tolerances. Typically, such a refrigerant filter drier unit includes a desiccant bed of beads of a suitable desiccant material, such as alumina, activated carbon, or other materials known to those skilled in the art. Further, filter pads of a suitable inorganic fibrous material is usually provided for removing of particulate material from the refrigerant.
Filter drier units, such as shown in U.S Pat. No. 4,364,756, are intended for use in a refrigerant suction line in which gaseous or vapor refrigerant enters the filter, passes through the filter and desiccant media, and is returned to the suction side of the refrigeration compressor.
In other types of refrigerant filter driers, such as shown in U.S Pat. Nos. 3,815,752 and 4,209,401, refrigerant enters the housing of the filter drier unit and impinges directly on a perforate plate in front of a bed of desiccant beads. A fibrous filter is provided downstream of the desiccant. Additionally, bi-directional filter drier units are known for use in heat pumps or the like where the flow of the refrigerant is reversed, depending on whether the heat pump is operating in its heating or cooling mode. Such bi-directional flow of filter drier units are shown in U S. Pat. Nos. 4,029,580 and 4,177,145. However, as was the case in regard to the single directional flow filter drier shown in the above-noted U.S Pat. Nos. 3,815,752 and 4,209,401, the refrigerant in the above-mentioned bi-directional filter drier units first came into contact with the bed of beaded desiccant prior to being filtered by the inorganic fibrous filter media.
In such filter drier units as described above, particularly wherein a liquid (as opposed to a gaseous) refrigerant is filtered, the impingement of the incoming jet of liquid refrigerant on the compacted bed of desiccant beads caused additional compaction and movement of the beads relative to one another, especially on startup and shutdown of the flow of refrigerant. This was true even if the desiccant beads were compacted and vibrated prior to assembly of the filter drier and even though the desiccant beads are maintained in their compacted state by means of a compression spring. Moreover, if any extra space or volume existed within the bed of desiccant beads, the impingement of the flow of liquid refrigerant causes movement of the beads relative to one another, known as roiling, and the relative movement of the hard desiccant beads causes small particles or flakes of the desiccant beads to flake off which in turn must be trapped by the downstream filters. Of course, as more of the desiccant beads flake off, more free space exists within the desiccant bed thereby to permit more movement of the desiccant beads relative to one another which encourages still more flaking. Thus, over a period of time, a substantial amount of the desiccant beads would be removed by flow erosion and these flaked desiccant particles would tend to become trapped on the downstream filter pads thus, at least in part, blocking the flow of refrigerant through the filter drier unit and increasing the pressure drop across the filter drier unit. Additionally, if pieces of the flaked off desiccant escape through the downstream filter means, these hard particles of desiccant could do damage to compressor parts and other close tolerance, movable parts (e.g., the thermal expansion valve) within the refrigerant unit. Additionally, an increased pressure drop across the filter drier unit may result which could adversely affect the operation of the refrigeration system.
Thus, there has been a longstanding need for a filter drier unit for application in a liquid refrigerant line in which the roiling effect of the compacted desiccant beads is minimized.